docs: def tail(self, stream='stdout', num_lines=10):
          """ Tail a specified stream (stdout or stderr) by num_lines. """
          target = self._map_string_to_file(stream)
          if not target:  # no current temp file
              last_run = self.backend.get_latest_run_log(self.parent_job.job_id,
                                                         self.name)
              if not last_run:
                  return None
              return self._tail_string(last_run['tasks'][self.name][stream],
                                       num_lines)
          else:
              return self._tail_temp_file(target, num_lines)